Hydraulic control valves of the type normally operated by application of hydraulic pressure at opposite ends of a valve spool commonly also include a control handle or lever for use in manually controlling the position of the valve spool and thereby overriding the pilot valves commonly used as the primary valve control mechanism.
An example of the use of such control handles is in valves used to control movement of an articulated boom of an aerial lift. Aerial lifts commonly include three or more control valves controlling the supply of hydraulic fluid to hydraulic cylinders and hydraulic motors. These hydraulic cylinders and hydraulic motors are used to control the movement of the articulated boom. The control valves are normally mounted at the base of the boom, and a control device is mounted in the operator's bucket. The operator uses the control device to control pilot valves in turn controlling operation of the control valves. The pilot valves control the delivery of hydraulic fluid to the opposite ends of the valve spools of the control valves and control the relative position of the valve spools.
It is also necessary to provide a means for controlling the bucket position from the ground, and this means must be capable of overriding the control lever in the bucket. In the event the control handle in the bucket jams or malfunctions, an operator on the ground can control movement of the bucket by manipulation of the override control handle at the control valve. The override control must also permit the operator to accurately control the position of the bucket. One of the prior art arrangements for use in providing an override control for a hydraulic control valve includes a control handle pivotally connected to the control valve and operably connected to the valve spool to move with the valve spool. Such an override control is illustrated in the Myers U.S. Pat. No. 2,946,196, issued July 26, 1960. In other valve arrangements, a rack and pinion is provided for operably connecting a control lever to the valve spool. In other similar override control levers, the control handle and valve spool are connected such that there is lost motion between the valve spool and the control lever. With override control valves of the type shown in Myers or including a rack and pinion arrangement, during normal operation of the control valve, movement of the valve spool causes consequent movement of the override control lever. Movement of the valve spool is impeded by frictional resistance in the control lever mechanism and by inertia of the mass of the control handle. This resistance or friction limits accurate control of the hydraulic control valves during normal operation of the valves.
While those arrangements having a lost motion connection between the valve spool and the control handle do not generate frictional forces resisting movement of the valve spool, the lost motion arrangements do not permit the operator sufficient control over the articulated boom when the control valves are being operated by the override control lever.
Attention is also directed to the Schmiel U.S. Pat. No. 4,195,551, issued Apr. 1, 1980; the Singleton U.S. Pat. No. 4,049,235, issued Sept. 20, 1977; the Knutson et al. U.S. Pat. No. 4,011,891, issued March 15, 1977; and the Schwerin U.S. Pat. No. 3,891,182, issued June 24, 1975.
Attention is further directed to the Toth U.S. Pat. No. 3,737,140, issued June 5, 1973; the Badke U.S. Pat. No. 3,269,412, issued Aug. 30, 1966; the Johnson U.S. Pat. No. 2,984,116, issued May 16, 1961; the Cantalupo U.S. Pat. No. 3,515,250, issued June 2, 1970; the Taylor U.S. Pat. No. 3,311,128, issued Mar. 28, 1967; the Newberry U.S. Pat. No. 2,932,978 issued Apr. 19, 1960; the Coles U.S. Pat. No. 4,285,296, issued Aug. 25, 1981; and the Hill U.S. Pat. No. 2,980,391, issued Apr. 28, 1961.